Dental plaque is a precursor of periodontal disease, one of the most common bacterial infections of man. The factors that regulate the colonization of plaque by periodontal pathogens are poorly understood. Adherence of the pathogenic bacteria to early plaque bacteria is an important first step in the colonization process. In this proposal, the adherence of Bacteroides gingivalis (a putative periodontal pathogen) to Streptococcus sanguis (an early plaque species) will be investigated. The bacteroides will be radiolabelled and binding to S. sanguis immobilized on a solid support measured. The nature of the binding will be ascertained by testing for inhibition with various physical and chemical agents. Interacting molecules will be visualized by incubating labelled organisms of one bacterial species with surface molecules extracted from its binding partner and separated by electrophoresis and blotting. The bacterial molecules involved in binding will be isolated by various chromatographic and electrophoretic techniques and/or recombinant DNA methodologies. After chemical characterization of the interacting molecules, they will be used for the production of monocional antibodies. Antibodies that inhibit binding of the homologous bacteria will be used to define the functional domains of the interacting molecules. Thus, these studies will begin to dissect the interbacterial interactions important in the colonization of the oral cavity by pathogenic organisms. This information will enhance our understanding of how periodontal pathogens establish themselves in the mouth. The elucidation of these mechanisms may allow the development of measures to prevent the colonization of these bacteria thus inhibiting the development of periodontal disease.